Whether you can use the OBi100 for a new provider depends on the provider that you choose. Some providers, such as Vonage, require that you use their preconfigured ata.
Some providers package their services with a flat rate, some have both flat rate and pay per minute, others are strictly pay per minute. For incoming calls providers often provide numbers with a choice of unlimited incoming or per minute pricing. In the U.S. and Canada you also need to allow for 911 emergency calling service which carries a small monthly fee.
CallCentric is fairly unique in that they provide a free incoming number located in certain parts of New York State. Incoming numbers, though, in general are not very expensive.
For outgoing calls, 600 minutes at 0.01 per minute is $6 per month. 600 minutes at 0.02 per minute is $12 per month.
Three providers that I would look at are CallCentric,
Voip.ms, and Anveo. In addition, Callwithus is also very good, but only provides outbound calling for U.S. customers.
There are others. With the above providers you can certainly use your own OBi100. You can even configure more than one provider on the adapter. You can configure two providers with both incoming and outgoing calls plus you can configure additional outgoing only providers if you wish.
